Direct quotations should constitute no more than ten percent of the total words.
Explanation:
A direct quotation is a report of the exact same words of an author and is placed inside quotation marks (") in a written work. They differ from the indirect quotation because in those you paraphrase, write with your own words, what the author said.
If your quotations constitute more than ten percent of the research paper you would make your own paper hard to read because you´ll move from one quotation to another. The quotation must be used only to support your own ideas or refute the other author´s ones.
The correct option is D. The statement in option D reveals that the youthfulness which the four old people gained was very momentarily, it soon passed away and they were back to square one.